I have been using Avast on my PC and Android for a number of years now, and i must say i am become fed up of Avast mobile security app. So much so that i have tested out a number of other AVs for my Android.
Reason: Annoying ads, too many unnecessary add ons on the mobile app and to top it all off the Anti-Theft features hardly ever work. The locate phone feature usually works on second attempt and take photos feature hardly ever works.
So far the best i have found is Norton (surprisingly!), but the price of £29.99/year is too high in my opinion for a mobile app.
Also, check out these malware detection results and you’ll see Avast does not do very well compared to others…
http://www.tomsguide.com/us/norton-mobile-security,review-2101.html